Method for producing salts having hydridocyanoborate anions

ABSTRACT

The invention relates to a method for producing alkali metal salts having monohydrido-tricyanoborate anions from alkali metal monofluorotricyanoborates, and to a method for producing alkali metal salts having dihydrido-dicyanoborate anions from alkali metal difluorodicyanoborates.

The invention relates to a process for the preparation of alkali metalsalts having monohydridotricyanoborate anions from alkali metalmonofluorotricyanoborates, and to a process for the preparation ofalkali metal salts having dihydridodicyanoborate anions from alkalimetal difluorodicyanoborates.

Alkali metal salts having monohydridotricyanoborate anions are knownfrom published specification WO 2012/163489 and serve, for example, asstarting materials for the synthesis of monohydridotricyanoborate saltshaving preferably organic cations. Ionic liquids of this type havingmonohydrido-tricyanoborate anions are suitable, for example, aselectrolyte component for electrochemical cells, in particular for dyesolar cells. WO 2012/163489 also describes the synthesis of these alkalimetal salts, for example by the processes of Claims 4 to 6.

In these processes, the starting materials employed are either alkalimetal tetracyanoborates or alkali metal tetrahydridoborates.

B. Györi et al, Journal of Organometallic Chemistry, 255, 1983, 17-28,describe, for example, the isomerisation of sodiumtriisocyanohydridoborate (adduct with 0.5 mol of dioxane) to sodiummonohydridotricyanoborate in boiling n-dibutyl ether.

Alkali metal salts having dihydridodicyanoborate anions are known frompublished specifications WO 2012/163490 and WO 2012/163488 and likewiseserve as starting materials for the synthesis of dihydridodicyanoboratesalts having preferably organic cations, which are suitable, forexample, for use as electrolyte component in electrochemical cells, inparticular dye solar cells.

WO 2012/163488 describes processes for the preparation of alkali-metaldiydridodicyanoborates, in which either an alkali metaltetrahydridoborate or an alkali metal trihydridocyanoborate are used asstarting materials.

A synthesis of lithium [BH₂(CN)₂] is known, for example, from B. Györiet al, Journal of Organometallic Chemistry, 1983, 255, 17-28, whereoligomeric 1/n (BH₂CN)_(n) is reacted with LiCN*CH₃CN in dimethylsulfide.

A synthesis of sodium [BH₂(CN)₂] is known, for example, from B. F.Spielvogel et al, Inorg. Chem. 1984, 23, 3262-3265, where a complex ofanilline with BH₂CN is reacted with sodium cyanide. Tetrahydrofuran isdescribed as solvent. P. G. Egan et al., Inorg. Chem. 1984, 23,2203-2204, also describe the synthesis of the dioxane complexNa[BH₂(CN)₂]*0.65(dioxane) based on the papers by Spielvogel et al.using another work-up variant.

Y. Zhang and J. M. Shreeve, Angew. Chem. 2011, 123, 965-967, describe,for example, the use of Ag[BH₂(CN)₂] for the preparation of ionicliquids having the dihydridodicyanoborate anion.

However, there continues to be a need for economical alternativesynthetic methods for the preparation of alkali metalmonohydridotricyanoborates or alkali metal dicyanodihydridoborates.

The object of the present invention is therefore to develop alternativepreparation processes which start from readily accessible andcomparatively cheaper starting materials. In particular, this need isfor the synthesis of alkali metal monohydridotricyanoborates.

Surprisingly, it has been found that alkali metalmonofluorotricyanoborates are excellent starting materials for thesynthesis of the desired monohydridotricyanoborates, which are readilyaccessible.

Surprisingly, it has been found that alkali metal difluorodicyanoboratesare excellent starting materials for the synthesis of the desireddihydridodicyanoborates, which are readily accessible.

This finding is surprising and unforeseeable, since boranes aregenerally strong acceptors for fluoride and the B—F bond formed isgenerally stronger than a B—H bond. N. N. Greenwood and A. Earnshaw,Chemistry of the Elements, Elsevier Science Ltd., 1997, indicate thebond energy E_((B—F)) as 646 kJ/mol, whereas the bond energy E_((B—H) isdescribed as 381 kJ/mol.

The invention therefore relates to a process for the preparation ofcompounds of the formula I

[Me]⁺[BH_(n)(CN)_(4-n)n]⁻  I,

whereMe denotes an alkali metal andn denotes 1 or 2,by reaction of a compound of the formula II

[Me¹]⁺[BF_(n)(CN)_(4-n)]⁻  II,

where Me¹ denotes an alkali metal, which may be identical to ordifferent from Me, andn denotes 1 or 2, where n is identical in formula I and formula II, witheither

-   a) an alkali metal or alkaline-earth metal Me², where an alkali    metal Me² may be identical to or different from Me or Me¹;    -   or a metal alloy Me²/Me or Me²/Me¹, where, in the case where Me²        is an alkali metal, this alkali metal Me² is different from Me        or Me¹; in an inert-gas atmosphere and    -   in the presence of a medium which is either capable of        generating and/or stabilising solvated electrons or is capable        of forming an anion free radical, if necessary with addition of        a proton source, and    -   a metal cation exchange in the case where neither Me² nor Me¹        corresponds to Me,    -   or-   b) an alkali metal hydride of the formula III

Me³H  III

-   -   in an inert-gas atmosphere,    -   where Me³ may be identical to or different from Me or Me¹,        without or in the presence of an F⁻-affinitive electrophilic        reagent, and subsequent metal cation exchange in the case where        neither Me³ nor Me¹ corresponds to Me.

The process according to the invention takes place in an inert-gasatmosphere, where the inert gases are preferably nitrogen or argon.

Alkali metals are the metals lithium, sodium, potassium, caesium orrubidium. Preferred alkaline-earth metals are calcium or barium.

In compounds of the formula I, Me is preferably sodium or potassium,particularly preferably potassium.

Accordingly, the process according to the invention is preferablysuitable for the synthesis of sodium monohydridotricyanoborate orpotassium monohydrido-tricyanoborate and for sodiumdihydridodicyanoborate or potassium dihydridodicyanoborate.

The compounds of the formula II are commercially available or accessibleby known synthetic processes. In the compounds of the formula II, Me¹can be an alkali metal selected from the group lithium, sodium,potassium, caesium or rubidium, which is selected independently of thealkali metal of the end product of the formula I. Me¹ in formula II maybe identical to or different from Me in formula I.

In compounds of the formula II, Me¹ is preferably sodium or potassium.

The preparation of the compounds of the formula II, as described aboveor as preferably described, can be carried out, for example, by reactionof an alkali metal cyanide with boron trifluoride etherate, as describedin WO 2004/072089.

Alternatively, the compounds of the formula II in which n denotes 1 or 2can be prepared by reaction of an alkali metal tetrafluoroborate with atrialkylsilyl cyanide. The reaction of a tetrafluoroborate withtrimethylsilyl cyanide is described, for example, in B. H. Hamilton etal., Chem. Commun., 2002, 842-843 or in E. Bernhardt et al., Z. Anorg.Allg. Chem. 2003, 629, 677-685.

Trialkylsilyl cyanides are commercially available or are accessible byknown synthetic processes.

The alkyl groups of the trialkylsilyl cyanide may be identical ordifferent. The alkyl groups of the trialkylsilyl cyanide have 1 to 10 Catoms, preferably 1 to 8 C atoms, particularly preferably 1 to 4 Catoms. The alkyl groups of the trialkylsilyl cyanide are preferablyidentical in the case of alkyl groups having 1 to 4 C atoms. An alkylgroup of the trialkylsilyl cyanide is preferably different if it is analkyl group of 5 to 10 C atoms or of 5 to 8 C atoms. Suitable examplesof trialkylsilyl cyanides are trimethylsilyl cyanide, triethylsilylcyanide, triisopropylsilyl cyanide, tripropylsilyl cyanide,octyldimethylsilyl cyanide, butyldimethylsilyl cyanide,t-butyldimethylsilyl cyanide or tributylsilyl cyanide.

Particular preference is given to the use of trimethylsilyl cyanide,which is commercially available or can also be prepared in situ.

The trialkylsilyl cyanide can also be prepared in situ for thepreparation of the compounds of the formula II. Many preparation methodshave been described for the synthesis of trialkylsilyl cyanide.

Trialkylsilyl cyanide can be prepared, for example, from an alkali metalcyanide and a trialkylsilyl chloride. EP 76413 describes that thisreaction was carried out in the presence of an alkali metal iodide andin the presence of N-methylpyrrolidone.

EP 40356 describes that this reaction was carried out in the presence ofa heavy-metal cyanide.

WO 2008/102661 describes that this reaction was carried out in thepresence of iodine and zinc iodide.

WO 2011/085966 describes that this reaction can be carried out in thepresence of an alkali metal iodide or fluoride and optionally iodine.Preference is given here to the use of sodium cyanide and sodium iodideor potassium cyanide and potassium iodide, where the alkali metal iodideis preferably added in a molar amount of 0.1 mol, based on 1 mol ofalkali metal cyanide and trialkylsilyl chloride. In general, thisprocess for the preparation is based on the description by M. T. Reetz,I. Chatziiosifidis, Synthesis, 1982, p. 330; J. K. Rasmussen, S. M.Heilmann and L. R. Krepski, The Chemistry of Cyanotrimethylsilane in G.L. Larson (Ed.) “Advances in Silicon Chemistry”, Vol. 1, p. 65-187, JAIPress Inc., 1991 or WO 2008/102661.

The in-situ generation of trialkylsilyl cyanide for the synthesis of thecompounds of the formula II is preferably carried out in accordance withthe reaction conditions which are indicated in WO 2011/085966.

Working examples of the synthesis of representative compounds of theformula II are indicated in the example part.

Irrespective of which embodiment of process variant a) or b) of theprocess according to the invention is selected, it is preferred if thereaction of the reactants is followed by a purification step in order toseparate the end product of the formula I, as described above, off fromby-products or reaction products.

Suitable purification steps include the separation of readily volatilecomponents by distillation or condensation, extraction with an organicsolvent or a combination of these methods. Any known separation methodcan be used for this purpose or combined.

The invention therefore furthermore relates to the process according tothe invention, as described above, where the reaction according toprocess variant a) or b) is followed by a purification step.

Should a metal cation exchange be necessary after the reaction of thecompound of the formula II with the reactants indicated, as describedabove and below, has taken place, since the corresponding alkali metalcation Me for the target product of the formula I is not yet present inthe reaction mixture, it is preferred in an embodiment of the inventionif the metal cation exchange takes place during the purification step.

The metal cation exchange is preferably an alkali metal cation exchange.

A preferred method for the metal cation exchange or preferably thealkali metal cation exchange is, for example, the reaction of thereaction mixture obtained in accordance with variant a) or variant b)with a corresponding carbonate (Me)₂CO₃ and/or a correspondinghydrogencarbonate MeHCO₃, where Me corresponds to the alkali metal Me ofthe desired end product of the formula I.

If, for example, extraction is selected as purification step, an organicsolvent is added to the aqueous reaction mixture in this case. Theaddition of the carbonate (Me)₂CO₃ and/or the hydrogencarbonate MeHCO₃to the aqueous phase of the original reaction mixture and the suitablechoice of solvent for the end product of the formula I facilitates in anadvantageous manner the separation of reaction products and by-productsfrom the end product of the formula I.

The invention therefore furthermore relates to the process according tothe invention, as described above, where the metal cation exchange,preferably the alkali metal cation exchange, takes place during thepurification step.

The invention therefore furthermore relates to the process according tothe invention, as described above, where the metal cation exchange iscarried out by reaction with the compound (Me₂)CO₃ and/or the compoundMeHCO₃, where Me corresponds to the alkali metal Me of the desired endproduct of the formula I.

Irrespective of which embodiment of process variant a) or b) of theprocess according to the invention is selected, it is preferred if thereaction of the compound of the formula II, as described above ordescribed as preferred, takes place in the presence of an organicsolvent. The solvent respectively suitable for process variant a) or b)is indicated below.

The invention therefore furthermore relates to the process according tothe invention, as described above, where the reaction of the compound ofthe formula II, as described above or described as preferred, both invariant a) and also in variant b), takes place in the presence of anorganic solvent.

In process variant a) of the process according to the invention, asdescribed above, a compound of the formula II, as described above, isreacted with an alkali metal or an alkaline-earth metal Me². If themetal Me² selected for use is an alkali metal, this may be identical toor different from the alkali metal cation of the compound of the formulaII and may also be identical to or different from the alkali metalcation of the target product of the formula I.

If the alkali metal Me² used is different from Me¹ and Me, this reactionmust be followed by an alkali metal cation exchange as process step inorder to obtain the process end product of the formula I. If analkaline-earth metal Me² is used, this reaction must be followed by ametal cation exchange as process step in order to obtain the process endproduct of the formula I. In a preferred process variant, the metal Me²is an alkali metal, as described above.

Alternatively, the process end product may also be a salt mixture ofhydridocyanoborates with the alkali metal cations [Me]⁺, [Me¹]⁺ and/orthe cation [Me²]⁺ or [Me²]²⁺. Depending on the desired subsequentreaction, separation of the salt mixture is not automatically necessary.The metal cation exchange to give the single process end productcontaining Me is then not necessary.

If a metal alloy Me²/Me or Me²/Me¹ is used in process variant a) a metalcation exchange is likewise necessary in order to obtain a singleprocess end product containing the alkali metal Me.

The invention furthermore also relates to the process, as describedabove, in which, in process variant a), the medium for the generationand/or stabilisation of solvated electrons is selected from liquidammonia, hexamethylphosphoric triamide (HMPA), amines,α,ω-diaminoalkanes, alcohols or diols.

Suitable amines are, for example, methylamine or ethylamine.

Suitable α,ω-diaminoalkanes are, for example, ethane-1,2-diamine,propane-1,3-diamine, butane-1,4-diamine or hexane-1,6-diamine.

Suitable alcohols are, for example, ethanol, n-propanol, i-propanol orbutanol.

Suitable diols are, for example, ethylene glycol or 1,4-butanediol.

The preferred medium for the generation and/or stabilisation of solvatedelectrons is liquid ammonia.

Accordingly, the invention furthermore relates to a process as describedabove, characterised in that the medium for the generation and/orstabilisation of solvated electrons is liquid ammonia.

The invention furthermore also relates to the process, as describedabove, where, in process variant a), the medium which is capable offorming anion free radicals is selected from condensed aromaticcompounds.

Condensed aromatic compounds form with an alkali metal Me² an anion freeradical which acts as strong reducing agent.

Suitable condensed aromatic compounds are, for example, naphthalene,indene, fluorene, acenaphthylene, anthracene, phenanthrene or alsopolycyclic aromatic condensed hydrocarbons, for example tetracene,pentacene or hexacene.

The condensed aromatic compound selected is preferably naphthalene.

Accordingly, the invention furthermore relates to a process as describedabove, characterised in that the medium which is capable of forminganion free radicals is naphthalene.

In an embodiment of process variant a), a compound of the formula II, asdescribed above, is reacted with an alkali metal Me² in liquid ammonia[NH₃(I)]. Lithium in NH₃(I), sodium in NH₃(I) or potassium in NH₃(I) ispreferably used. Sodium in NH₃(I) or potassium in NH₃(I) is particularlypreferably used.

Since the reaction with liquid NH₃ as only proton source is relativelyslow, it is advantageous in this reaction procedure if a further protonsource is added after the reaction with an alkali metal Me². A suitableproton source is selected, for example, from methanol, ethanol, butanol,aqueous mixtures of these alcohols, water or ammonium salts.

Suitable ammonium salts are, for example, ammonium chloride, ammoniumsulfate or triethylammonium chloride.

In accordance with the invention, it is advantageous to use water asproton source.

The conditions of this embodiment of process variant a) also apply tothe reaction of an alkaline-earth metal or a metal alloy Me²/Me orMe²/Me¹ in liquid ammonia. A preferred alkali metal alloy for theprocess according to the invention is Na/K.

The invention therefore furthermore relates to the process according tothe invention, as described above, where the proton source is water.

The metal Me² employed or the metal alloy Me²/Me or Me²/Me¹ employed ispreferably free from protecting agents which surround the metal or metalalloy, for example oil or paraffin.

It is also preferred in this embodiment of process variant a), asdescribed above, if the reaction takes place in the presence of anorganic solvent. Suitable solvents are diethyl ether, methyl t-butylether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,2-dimethoxyethane ordiglyme. A preferred solvent is tetrahydrofuran.

Without being tied to the theory, the reaction in this embodiment ofprocess variant a) in liquid ammonia will proceed in one or more steps,where the different anion species are able to form and are thenultimately converted into the monohydridotricyanoborate ordihydridodicyanoborate by reaction with the proton source.

It is therefore advantageous in this embodiment of process variant a) ifthe proton source is added separately or in the mixture with the organicsolvent.

The addition of the proton source is preferably carried out attemperatures between −20° C. and 25° C., particularly preferably at 0°C.

It is therefore advantageous for this embodiment of process variant a)if the compound of the formula II, as described above or described aspreferred, is initially introduced in a reaction vessel which issuitable for liquid ammonia, ammonia is condensed in at −78° C., and themetal Me² or the metal alloy Me²/Me or Me²/Me¹ is subsequently added inan inert-gas atmosphere. It may then be advantageous to stir thisreaction mixture at −78° C. to −40° C. for 10 to 120 minutes and toallow the reaction mixture to warm to room temperature after the metalhas been consumed. Corresponding precautionary measures for the ammoniaevaporating must be observed.

After addition of the proton source, as described above, a metal cationexchange may follow if the corresponding alkali metal cation Me for thetarget product of the formula I is not yet present in the reactionmixture under the conditions, as described above.

In this embodiment of process variant a), it is preferred if thereaction is followed by a purification step in the form of anextraction. Preferred solvents can be selected from the grouptetrahydrofuran, acetone, nitrile, such as, for example, acetonitrile,alcohol, such as, for example, methanol, ethanol or butanol, dialkylether, such as, for example, diethyl ether, monoglyme or diglyme.

Tetrahydrofuran is particularly preferably employed in this embodimentof process variant a).

In another embodiment of process variant a), a compound of the formulaII, as described above, is reacted with a metal Me² or a metal alloyMe²/Me or Me²/Me¹ in the presence of naphthalene. In this variant, themetal Me² is an alkali metal, as defined above, or the metal alloy is analkali metal alloy, as defined above.

Without being tied to the theory, the reaction in this alternativeembodiment of process variant a) will proceed in one or more steps,where different anion species are able to form and are then ultimatelyconverted into the monohydridotricyanoborate or dihydridodicyanoborateby reaction with a suitable proton source.

Suitable as proton source are, for example, methanol, ethanol, butanol,aqueous mixtures of these alcohols, aqueous solutions of carboxylicacids or mineral acids, water, or ammonium salts.

Suitable carboxylic acids are acetic acid, formic acid, glycolic acid ortartaric acid.

Suitable mineral acids are hydrochloric acid, sulfuric acid, nitric acidor phosphoric acid.

Suitable ammonium salts are ammonium chloride, ammonium sulfate ortriethylammonium chloride.

It is advantageous in accordance with the invention to use water asproton source.

The invention therefore furthermore relates to the process according tothe invention, also in this alternative process variant a), as describedabove, where the proton source is water.

It is likewise preferred in this alternative embodiment of processvariant a), as described above, if the reaction takes place in thepresence of an organic solvent. Suitable solvents are diethyl ether,tetrahydrofuran, 2-methyltetrahydrofuran, or 1,2-dimethoxyethane. Apreferred solvent is tetrahydrofuran.

It is therefore advantageous in this embodiment of process variant a) ifthe proton source is added in the organic solvent. The addition of theproton source is preferably carried out at temperatures between −20° C.and 25° C., particularly preferably at 0° C.

It is advantageous for this alternative embodiment of process variant a)if naphthalene is added to a solution of the compound of the formula II,as described above or described as preferred, in a suitable organicsolvent and the alkali metal Me² or the alkali metal alloy Me²/Me orMe²/Me¹ is subsequently added in excess in an inert-gas atmosphere. Thesuitable temperature range is 10° C. to 80° C., the reaction ispreferably carried out at room temperature. It is advantageous if thesame organic solvent is used for both steps.

The reaction of the compound of the formula II with Me²/naphthalene ispreferably carried out at temperatures between 10° C. and 60° C.,particularly preferably at room temperature. The reaction must becarried out in an inert atmosphere, preferably with exclusion of waterand oxygen. Conditions for the exclusion of water and oxygen aredescribed below and preferably also apply to this process variant.

After addition of the proton source, as described above in general termsand also for the first embodiment of process variant a), a metal cationexchange may follow if the corresponding alkali metal cation Me for thetarget product of the formula I is not yet present in the reactionmixture under the conditions, as described above.

In this embodiment of process variant a), it is preferred if thereaction is followed by a purification step in the form of anextraction. A preferred solvent for this purpose is tetrahydrofuran,dialkyl ether, acetone or acetonitrile. Tetrahydrofuran is particularlypreferably employed in this embodiment of process variant a).

In this embodiment of process variant a), it is advantageous if thecompound of the formula II, as described above or described aspreferred, is taken up in an alcohol or in a diol, preferably inethanol, and the alkali metal Me² or the alkali metal alloy Me²/Me orMe²/Me¹ is subsequently added in an inert-gas atmosphere. It may then beadvantageous to stir this reaction mixture at −40° C. to 140° C.,preferably at 0° C. to 80° C., for 10 minutes to a few hours and to workup the reaction mixture in accordance with the teaching of Example 10after the alkali metal has been consumed. It is advantageous in thisprocess variant to neutralise the metal alkoxide formed in excess usingmineral acids, for example aqueous hydrochloric acid, before asubsequent metathesis reaction.

In process variant b) of the process according to the invention, asdescribed above, a compound of the formula II, as described above, isreacted with an alkali metal hydride Me³H in an inert-gas atmosphere.The alkali metal cation [Me³]⁺ may be identical to or different from thealkali metal cation of the compound of the formula II and may also beidentical to or different from the alkali metal cation of the targetproduct of the formula I. If the alkali metal Me³ used is different fromMe¹ and Me, this reaction must necessarily be followed by an alkalimetal cation exchange as process step.

In an embodiment of process variant b), a compound of the formula II, asdescribed above, is reacted with an alkali metal hydride Me³H in thepresence of an F⁻-affinitive electrophilic reagent.

Without being tied to the theory, the mechanism of the nucleophilicsubstitution reaction is assumed for process variant b).

It has been found that the addition of an electrophilic reagent whichhas good affinity to F⁻ accelerates the substitution.

The term “affinity to F⁻” means that the reagent used preferably forms abond to the F⁻. The bond here can be a covalent bond or also a bondwhich arises through electrostatic interaction.

In a preferred embodiment of process variant b), the (F⁻)-affinitiveelectrophilic reagent is a lithium salt or a magnesium salt.

Suitable lithium salts are lithium bromide, lithium iodide, lithiumchloride, lithium triflate, lithium perchlorate or lithiumtetrafluoroborate.

A suitable magnesium salt is magnesium triflate.

In a particularly preferred embodiment of process variant b), lithiumbromide is employed as electrophilic reagent.

The invention therefore furthermore relates to the process according tothe invention, as described above, where the (F⁻)-affinitiveelectrophilic reagent is a lithium salt or a magnesium salt.

The invention therefore furthermore relates to the process according tothe invention, as described above, where the (F⁻)-affinitiveelectrophilic reagent is lithium bromide.

The reaction of the compounds of the formula II, as described above,with the alkali metal hydride of the formula III is preferably carriedout in the presence of an organic solvent, for example in the presenceof ethers. Preferred ethers are tetrahydrofuran, diethyl ether, methylt-butyl ether or dimethoxyethane. Tetrahydrofuran is particularlypreferably used.

The reaction according to the invention in accordance with processvariant b) preferably takes place at temperatures between 10° C. and200° C., in particular between 15° C. and 150° C., particularlypreferably at 100° C. to 150° C., very particularly preferably at 80° C.The reaction takes place in an inert-gas atmosphere, preferably withexclusion of water and oxygen. Conditions for the exclusion of water andoxygen are described below and preferably also apply to this processvariant.

It is preferred in this process variant b) if the work-up step, asdescribed above, includes a combination of various separation methods.

It is, for example, preferred to decompose the possible excess ofhydride of the formula III, as described above, by addition of water oran aqueous alcoholic solution of methanol, ethanol, isopropanol orbutanol and to remove all volatile constituents under reduced pressure.

It is furthermore preferred to take up the reaction product obtained inan organic solvent and to remove the by-products by extraction withwater or by filtration. In this step, the alkali metal cation exchangecan also be carried out correspondingly, as described in detail above.

However, it is advantageous in process variant b) if the alkali metalcation [Me³]⁺ corresponds to the metal cation of the end product of theformula I.

Suitable organic solvents are tetrahydrofuran, dialkyl ethers, such as,for example, diethyl ether, acetonitrile or acetone.

It is therefore advantageous for this embodiment of process variant b)if the compound of the formula II, as described above or described aspreferred, are stirred with the compound of the formula III, asdescribed above, and a suitable solvent at the reaction temperatureindicated and is subsequently worked up.

The process according to the invention may then be followed by aclassical metathesis reaction, where a compound of the formula IV

[Kt]^(z+) z[BH_(n)(CN)_(4-n)]⁻  IV

in which[Kt]^(z+) is an inorganic or organic cation, z corresponds to the chargeof the cation andn denotes 1 or 2 and n has the same meaning as in the starting compoundof the formula I, as described above,is formed.

The invention therefore furthermore relates to a process for thepreparation of compounds of the formula IV

[Kt]^(z+) z[BH_(n)(CN)_(4-n)]⁻  IV,

where[Kt]^(z+) is an inorganic or organic cation,z corresponds to the charge of the cation andn denotes 1 or 2,by anion exchange, where a salt containing the cation [Kt]^(z+) isreacted with a compound of the formula I

[Me]⁺[BH_(n)(CN)_(4-n)]⁻  I,

prepared by the process according to the invention, as described above,where Me denotes an alkali metal and n has the same meaning as in thecompound of the formula IV.[Kt]^(z+) preferably has the meaning of an organic cation or aninorganic cation, where the cation [Kt]^(z+) does not correspond to thecation Me⁺ employed in the compound of the formula I andthe anion A of the salt containing [Kt]^(z+) denotes F⁻, Cl⁻, Br⁻, I⁻,HO⁻, [HF₂]⁻, [CN]⁻, [SCN]⁻, [R₁COO]⁻, [R₁OC(O)O]⁻, [R₁SO₃]⁻, [R₂COO]⁻,[R₂SO₃]⁻, [R₁OSO₃]⁻, [PF₆]⁻, [BF₄]⁻, [HSO₄]⁻, [NO₃]⁻, [(R₂)₂P(O)O]⁻,[R₂P(O)O₂]²⁻, [(R₁O)₂P(O)O]⁻, [(R₁O)P(O)O₂]²⁻, [(R₁O)R₁P(O)O]⁻,tosylate, malonate, which may be substituted by straight-chain orbranched alkyl groups having 1 to 4 C atoms, [HOCO₂]⁻ or [CO₃]²⁻, whereR₁ in each case, independently of one another, denotes a straight-chainor branched alkyl group having 1 to 12 C atoms and R₂ in each case,independently of one another, denotes a straight-chain or branchedperfluorinated alkyl group having 1 to 12 C atoms and whereelectroneutrality is taken into account in the formula of the salt KtA.

A perfluorinated linear or branched alkyl group having 1 to 4 C atomsis, for example, trifluoromethyl, pentafluoroethyl, n-heptafluoropropyl,iso-heptafluoropropyl, n-nonafluorobutyl, sec-nonafluorobutyl ortert-nonafluorobutyl. R₂ defines analogously a linear or branchedperfluorinated alkyl group having 1 to 12 C atoms, encompassing theabove-mentioned perfluoroalkyl groups and, for example, perfluorinatedn-hexyl, perfluorinated n-heptyl, perfluorinated n-octyl, perfluorinatedethylhexyl, perfluorinated n-nonyl, perfluorinated n-decyl,perfluorinated n-undecyl or perfluorinated n-dodecyl.

R₂ is particularly preferably trifluoromethyl, pentafluoroethyl ornonafluorobutyl, very particularly preferably trifluoromethyl orpentafluoroethyl.

R₁ is particularly preferably methyl, ethyl, n-butyl, n-hexyl orn-octyl, very particularly preferably methyl or ethyl.

Substituted malonates are, for example, the compounds—methyl or ethylmalonate.

The anion A of the of the salt containing [Kt]^(z+) is preferably OH⁻,Cl⁻, Br⁻, I⁻, [CH₃SO₃]⁻[CH₃OSO₃]⁻, [CF₃COO]⁻, [CF₃SO₃]⁻, [(C₂F₅)₂P(O)O]⁻or [CO₃]²⁻, particularly preferably OH⁻, Cl⁺, Br⁻, [CH₃OSO₃]⁻,[CF₃SO₃]⁻, [CH₃SO₃]⁻ or [(C₂F₅)₂P(O)O]⁻.

The organic cation for [Kt]^(z+) is selected, for example, from iodoniumcations, ammonium cations, sulfonium cations, oxonium cations,phosphonium cations, uronium cations, thiouronium cations, guanidiniumcations, tritylium cations or heterocyclic cations.

Preferred inorganic cations are metal cations of the metals from group 2to 12 or also NO⁺ or H₃O+⁺.

Preferred inorganic cations are Ag⁺, Mg²⁺, Cu⁺, Cu²⁺, Zn²⁺, Ca²⁺, Y³⁺,Yb³⁺, La³⁺, Sc³⁺, Ce³⁺, Nd³⁺, Tb³⁺, Sm³⁺ or complex (ligand-containing)metal cations which contain rare-earth, transition or noble metals, suchas rhodium, ruthenium, iridium, palladium, platinum, osmium, cobalt,nickel, iron, chromium, molybdenum, tungsten, vanadium, titanium,zirconium, hafnium, thorium, uranium, gold.

The salt-exchange reaction of the salt of the formula I with a saltcontaining [Kt]^(z+), as described above, is advantageously carried outin water, where temperatures of 0°-100° C., preferably 15-60° C., aresuitable. The reaction is particularly preferably carried out at roomtemperature (25° C.).

However, the above-mentioned salt-exchange reaction may alternativelyalso be carried out in organic solvents at temperatures between −30° and100° C. Suitable solvents here are acetonitrile, propionitrile, dioxane,dichloromethane, dimethoxyethane, dimethyl sulfoxide, tetrahydrofuran,dimethylformamide, acetone or alcohol, for example methanol, ethanol orisopropanol, diethyl ether or mixtures of the above-mentioned solvents.

In a further embodiment of the process according to the invention, thecompound of the formula II is prepared in advance in situ from an alkalimetal tetrafluoroborate and a trialkylsilyl cyanide, where thetrialkylsilyl cyanide used can in turn be prepared before this reactionin situ from an alkali metal cyanide and a trialkylsilyl chloride, asdescribed above.

The invention therefore furthermore relates to a process for thepreparation of compounds of the formula I, as described above ordescribed as preferred, where the compound of the formula II is preparedin situ.

The invention therefore furthermore relates to a process for thepreparation of compounds of the formula I

[Me]⁺[BH_(n)(CN)_(4-n)]⁻  I,

whereMe denotes an alkali metal andn denotes 1 or 2,by reaction of a compound of the formula V

[Me¹]⁺[BF₄]⁻  V,

where Me¹ denotes an alkali metal, which may be identical to ordifferent from Me,with a trialkylsilyl cyanide, where the alkyl group of the trialkylsilylcyanide in each case, independently of one another, denotes a linear orbranched alkyl group having 1 to 10 C atoms, preferably having 1 to 8 Catoms, very particularly preferably having 1 to 4 C atoms, to give acompound of the formula II

[Me¹]⁺[BF_(n)(CN)_(4-n)]⁻  II,

where Me¹ corresponds to the alkali metal of the compound of the formulaV andn denotes 1 or 2, where n is identical in formula I and formula II,where the conditions of the reaction are selected in such a way thatboth the water content and also the oxygen content are a maximum of 1000ppm, andreaction with either

-   a) an alkali metal or alkaline-earth metal Me², where an alkali    metal Me² may be identical to or different from Me or Me¹;    -   or a metal alloy Me²/Me or Me²/Me¹, where, in the case where Me²        is an alkali metal, this alkali metal Me² is different from Me        or Me¹; in an inert-gas atmosphere and    -   in the presence of a medium which is either capable of        generating and/or stabilising solvated electrons or is capable        of forming an anion free radical, if necessary with addition of        a proton source, and    -   a metal cation exchange in the case where neither Me² nor Me¹        corresponds to Me,    -   or-   b) an alkali metal hydride of the formula III

Me³H  III

-   -   in an inert-gas atmosphere,    -   where Me³ may be identical to or different from Me or Me¹,        without or in the presence of an electrophilic reagent which has        affinity to F⁻ and subsequent metal cation exchange in the case        where neither Me³ nor Me¹ corresponds to Me.

The reaction of the alkali metal tetrafluoroborate with trialkylsilylcyanide, as described above, preferably takes place in the presence of atrialkylsilyl chloride, trialkylsilyl bromide and/or trialkylsilyliodide, where the alkyl groups of the trialkylsilyl halide in each case,independently of one another, denote a straight-chain or branched alkylgroup having 1 to 10 C atoms. Examples of trialkylsilyl cyanides aredescribed above or described as preferred.

The alkyl groups of the trialkylsilyl halide may be identical ordifferent. The alkyl groups of the trialkylsilyl halide preferably have1 to 8 C atoms, particularly preferably 1 to 4 C atoms. The alkyl groupsof the trialkylsilyl halide are preferably identical in the case ofalkyl groups having 1 to 4 C atoms. An alkyl group of the trialkylsilylhalide is preferably different if it is an alkyl group of 5 to 10 Catoms or of 5 to 8 C atoms.

The trialkylsilyl halide is preferably a trialkylsilyl chloride.

Suitable trialkylsilyl chlorides are trimethylsilyl chloride (orsynonymously trimethylchlorosilane), triethylsilyl chloride,triisopropylsilyl chloride, tripropylsilyl chloride, octyldimethylsilylchloride, butyldimethylsilyl chloride, t-butyldimethylsilyl chloride ortributylsilyl chloride. Particular preference is given to the use oftrimethylsilyl chloride. Very particular preference is given to the useof trimethylsilyl chloride alone.

Suitable trialkylbromosilanes are trimethylbromosilane (or synonymouslytrimethylsilyl bromide), triethylsilyl bromide, triisopropylsilylbromide, tripropylsilyl bromide, octyldimethylsilyl bromide,butyldimethylsilyl bromide, t-butyldimethylsilyl bromide ortributylsilyl bromide. Particular preference is given to the use oftrimethylsilyl bromide in a mixture with trimethylsilyl chloride.

Suitable trialkyliodosilanes are trimethyliodosilane (or synonymouslytrimethylsilyl iodide), triethylsilyl iodide, triisopropylsilyl iodide,tripropylsilyl iodide, octyldimethylsilyl iodide, butyldimethylsilyliodide, t-butyldimethylsilyl iodide or tributylsilyl iodide. Particularpreference is given to the use of trimethylsilyl iodide in a mixturewith trimethylsilyl chloride.

The trialkylsilyl halide or a mixture of trialkylsilyl halides, asdescribed above or described as preferred, is particularly preferablyemployed in a total amount of 1 to 20 mol %, based on the amount oftrialkylsilyl cyanide employed. The trialkylsilyl halide or a mixture oftrialkylsilyl halides is particularly preferably employed in a totalamount of 3 to 12 mol %, based on the amount of trialkylsilyl cyanideemployed. The trialkylsilyl halide or a mixture of trialkylsilyl halidesis very particularly preferably employed in a total amount of 7 to 11mol %, based on the amount of trialkylsilyl cyanide employed.

The reaction can be carried out both in an open apparatus and also in aclosed apparatus.

It is preferred to mix the starting materials of the formula V, thetrialkylsilyl cyanide and optionally the trialkylsilyl chloride in aninert-gas atmosphere whose oxygen content is a maximum of 1000 ppm. Itis particularly preferred if the oxygen content is less than 500 ppm,very particularly preferably a maximum of 100 ppm.

The water content of the reagents and of the inert-gas atmosphere is amaximum of 1000 ppm. It is particularly preferred if the water contentof the reagents and of the atmosphere is less than 500 ppm, veryparticularly preferably a maximum of 100 ppm.

The conditions with respect to the water content and oxygen content donot apply to the further reaction after process variants a) or b) or tothe work-up after reaction of the compound of the formula II with thetrialkylsilyl cyanide has taken place.

All further explanations of embodiments of the reaction according to theinvention of the compound of the formula II to give compounds of theformula I, as described above, apply correspondingly in this respect tothis one-pot process with the starting material of the compound of theformula V and can be combined in this respect without restriction.

In the case of in-situ generation of the trialkylsilyl cyanide, theinvention relates to the following one-pot process.

The invention therefore furthermore relates to a process for thepreparation of compounds of the formula I

[Me]⁺[BH_(n)(CN)_(4-n)]⁻  I,

whereMe denotes an alkali metal andn denotes 1 or 2,by reaction of a compound of the formula V

[Me¹]⁺[BF₄]⁻  V,

where Me¹ denotes an alkali metal, which may be identical to ordifferent from Me,with alkali metal cyanide and trialkylsilyl chloride under theconditions of in-situ generation of trialkylsilyl cyanide, where thealkyl group of the trialkylsilyl chloride and also of the trialkylsilylcyanide formed in each case, independently of one another, denotes alinear or branched alkyl group having 1 to 10 C atoms, preferably having1 to 8 C atoms, particularly preferably having 1 to 4 C atoms, to give acompound of the formula II

[Me¹]⁺[BF_(n)(CN)_(4-n)]⁻  II,

where Me¹ corresponds to the alkali metal of the compound of the formulaV andn denotes 1 or 2, where n in is identical formula I and formula II, andreaction with either

-   a) an alkali metal or alkaline-earth metal Me², where an alkali    metal Me² may be identical to or different from Me or Me¹;    -   or a metal alloy Me²/Me or Me²/Me¹, where, in the case where Me²        is an alkali metal, this alkali metal Me² is different from Me        or Me¹; in an inert-gas atmosphere and    -   in the presence of a medium which is capable of generating        and/or stabilising solvated electrons or is capable of forming        an anion free radical, if necessary with addition of a proton        source, and    -   a metal cation exchange in the case where neither Me² nor Me¹        corresponds to Me,    -   or-   b) an alkali metal hydride of the formula III

Me³H  III

-   -   in an inert-gas atmosphere,    -   where Me³ may be identical to or different from Me or Me¹,        without or in the presence of an electrophilic reagent which has        affinity to F⁻ and subsequent metal cation exchange in the case        where neither Me³ nor Me¹ corresponds to Me.

The in-situ generation of trialkylsilyl cyanide preferably takes placein the presence of an alkali metal iodide and optionally iodine, asdescribed above. The in-situ generation of trialkylsilyl cyanideparticularly preferably takes place in the presence of an alkali metaliodide. The conditions of the reaction for the in-situ generation arealso selected in such a way that both the water content and also theoxygen content are less than 1000 ppm. The conditions mentioned aboveapply correspondingly.

The amount of alkali metal iodide is preferably 4 to 6 mol %, based onthe amount of alkali metal cyanide, or 3 to 5 mol %, based on the amountof trialkylsilyl chloride. The amount of alkali metal iodide isparticularly preferably 4.9 to 5.1 mol %, based on the amount of alkalimetal cyanide, or 3.9 to 4.1 mol %, based on the amount of trialkylsilylchloride.

The one-pot synthesis, as described above, is preferably carried out ina closed reaction vessel. During the reaction, a maximum pressure of 2.5bar generally arises.

All further explanations of embodiments of the reaction according to theinvention of the compound of the formula II to give compounds of theformula I, as described above, apply correspondingly in this respect tothis one-pot process with the starting material of the compound of theformula V and the in-situ generation of trialkylsilyl cyanide and can becombined in this respect without restriction. Trimethylsilyl cyanide isparticularly preferably generated in situ in the one-pot process.

The word choice “one-pot process” means that the compound of the formulaII formed as an intermediate, as described above or described aspreferred, is not isolated. It is also possible in the process variantof the “one-pot process” to separate off excess reactants and/orby-products and/or assistants, such as solvents, present.

The substances obtained are characterised by means of NMR spectra. TheNMR spectra are measured on solutions in deuterated acetone-D₆ or inCD₃CN on a Bruker Avance 500 spectrometer with deuterium lock. Themeasurement frequencies of the various nuclei are: ¹H: 500.1 MHz, ¹¹B:160.5 MHz and ¹³C: 125.8 MHz. The referencing is carried out using anexternal reference: TMS for ¹H and ¹³C spectra and BF₃.Et₂O— for ¹¹Bspectra.

EXAMPLE 1 One-Pot Synthesis of Sodium Monofluorotricyanoborate;Na[BF(CN)₃]

6.0 g (40.0 mmol) of sodium iodide, NaI, and 40.0 g (816.3 mmol) ofsodium cyanide, NaCN, are suspended in 20 ml of acetonitrile. 130 ml(1029 mmol) of trimethylsilyl chloride, (CH₃)₃SiCl, are added to thesuspension. The reaction mixture is stirred vigorously at roomtemperature, during which the reaction mixture is kept in a sealedvessel with exclusion of light until the conversion of NaCN into(CH₃)₃SiCN has taken place. The reaction time can be one to two days.The reaction can be monitored via ¹³C-NMR measurements. 16.0 g (145.4mmol) of sodium tetrafluoroborate, Na[BF₄], are then added. The reactionmixture is stirred and heated for a further 1.5 hours in a closedvessel, during which the oil-bath temperature is 100° C. During thereaction, (CH₃)₃SiF (boiling point 16° C.) forms. For this reason, thesystem is under pressure (max. 2.5 bar), and the reaction vessel must beopened carefully. After cooling to room temperature, crystals haveformed, and all volatile components are removed in vacuo. Alternatively,the solids Na[BF(CN)₃] and NaCl may also be filtered. The solid residueor the filter residue is extracted with 150 ml of acetone. Acetone isthen distilled off, and the residue is taken up in 70 ml oftetrahydrofuran (THF). After addition of 200 ml of dichloromethane, theproduct Na[BF(CN)₃] precipitates out and is filtered off and dried invacuo, giving 17.61 g (134.5 mmol) of Na[BF(CN)₃]. This corresponds to ayield of 93%, based on Na[BF₄].

¹⁹F-NMR (solvent: acetone-D₆), δ, ppm: −212.2 q, ¹J_(11B,19F)=44 Hz,¹J_(10B,19F)=14.5 Hz

¹¹B-NMR (solvent: acetone-D₆), δ, ppm: −17.8 d, ¹J_(11B,19F)=44 Hz.

NaI (0.60 g, 4.00 mmol) and NaCN (4.0 g, 81.6 mmol) are taken up inacetonitrile (2.0 ml), trimethylchlorosilane, (CH₃)₃SiCl (10.3 ml, 81.6mmol), is added, and the mixture is stirred overnight at roomtemperature in a sealed vessel with exclusion of light. Sodiumtetrafluoroborate, Na[BF₄](1.6 g, 14.54 mmol), and furthertrimethylsilyl chloride (2.5 ml, 19.79 mmol) are added to thesuspension. The reaction mixture is heated at 1000 (oil-bathtemperature) for 3 hours in a closed vessel (max. pressure 2.5 bar). Allvolatile constituents (trimethylsilyl chloride, trimethylsilyl fluoride,trimethylsilyl cyanide) are subsequently removed in vacuo. The residueis extracted with acetone (20 ml), and the filtrate is evaporated todryness in vacuo.

Yield: 1.8 g (13.75 mmol), corresponding to 95%, based on the borateemployed.

The ¹⁹F and ¹¹B NMR spectra are identical to those of Example A).

EXAMPLE 2 Synthesis of Sodium Monofluorotricyanoborate; Na[BF(CN)₃]

11.0 g (100 mmol) of sodium tetrafluoroborate, Na[BF₄], is initiallyintroduced in a flask with PTFE spindle (Young, London). 100 ml of themixture of trimethylsilyl cyanide, (CH₃)₃SiCN (75 mol %), trimethylsilylchloride, (CH₃)₃SiCl (15 mol %) and trimethylsilyl fluoride, (CH₃)₃SiF(10 mol %), obtained in Example 1 (these and similar mixtures arerecovered from the reactions described here during work-up) is added tothe sodium tetrafluoroborate. The flask is closed, and the reactionmixture is stirred at 900 (oil-bath temperature) for 4 hours. 20 ml offresh trimethylsilyl cyanide and 2 ml of trimethylsilyl chloride arethen added, and the reaction mixture is stirred at 800 (oil-bathtemperature) for a further 5 hours.

All volatile substances are then distilled off, and the residue is driedat 600 in vacuo for one day, giving 13.1 g (100 mmol) of Na[BF(CN)₃].

The ¹⁹F- and ¹¹B-NMR spectra are identical with those of Example 1.

EXAMPLE 3 Synthesis of Potassium Monofluorotricyanoborate; K[BF(CN)₃]

20.0 g (182 mmol) of sodium tetrafluoroborate, Na[BF₄], and 200 ml (1.5mol) of trimethylsilyl cyanide, (CH₃)₃SiCN, are initially introduced,and 20 ml (158 mmol) of trimethylchlorosilane, (CH₃)₃SiCl, are added tothis suspension. The reaction mixture is heated under reflux (oil-bathtemperature 65° C. to 95° C.) for 96 hours. All volatile substances arethen distilled off in vacuo. The mixture of trimethylsilyl cyanide,(CH₃)₃SiCN, trimethylsilyl chloride, (CH₃)₃SiCl, and trimethylsilylfluoride, (CH₃)₃SiF, is collected in a cold trap and can be employedanalogously to the mixture in Example 2 in a second synthesis. Theresidue is taken up in 100 ml of water, and hydrogen peroxide H₂O₂ (37%solution, about 200 ml) and K₂CO₃ (about 100 g) are carefully addeduntil the solution is virtually no longer coloured. The excess peroxideis destroyed by addition of K₂S₂O₅. The water is distilled off, and theresidue obtained is extracted with acetone (3×100 ml). The combinedorganic phases are reduced to 50 ml, and dichloromethane is then addeduntil K[BF(CN)₃] precipitates out. Filtration and drying in vacuo gives19.8 g (134.8 mmol) of K[BF(CN)₃]. The yield is 74%, based on sodiumtetrafluoroborate.

¹⁹F-NMR (solvent: acetone-D₆), δ, ppm: −212.08 q, ¹J_(11B,19F)=44.4 Hz.

¹¹B-NMR (solvent: acetone-D₆), δ, ppm: −17.88 d, ¹J_(11B,19F)=44.4 Hz.

The spectra are identical to those of Example 1 and correspond to thosefrom the literature [E. Bernhardt, M. Berkei, H. Willner, M. Schirmann,Z. Anorg. Allg. Chem., 2003, 629, 677-685].

Elemental Analysis:

found, %: C, 24.53, H, 0.00, N, 27.86;

calculated for C₃BFN₃K, %: C, 24.52, H, 0.00, N, 28.59.

EXAMPLE 4 Synthesis of Potassium Monohydridotricyanoborate; K[BH(CN)₃]

3.75 g of sodium fluorotricyanoborate (28.6 mmol) is initiallyintroduced in a flask with PTFE spindle (Young, London), and ammonia (40ml) is condensed in at −78° C. 1.32 g of sodium (57.4 mmol) issubsequently added with stirring in a counterstream of argon. Thereaction mixture is slowly warmed to room temperature, so that theammonia is able to escape. The residue is carefully taken up with aTHF/water mixture (200 ml of THF, 50 ml of water) at 0° C. K₂CO₃ (about5 g) is added until a clear phase separation is evident. Theseparated-off water phase is saturated with K₂CO₃ (about 50 g) andextracted with THF (3×50 ml). The combined THF phases are dried usingK₂CO₃ and evaporated to a residual volume of 10 ml. Virtually colourlesspotassium hydridotricyanoborate can be precipitated by addition ofCH₂Cl₂.

Yield: 2.38 g (18.5 mmol), 65%, based on the sodium fluorotricyanoborateemployed.

¹H{¹¹B}-NMR (solvent: acetonintrile D₃), δ, ppm: 1.77 s.

¹¹B-NMR (solvent: acetonitrile D₃), δ, ppm: −40.2 d, ¹J_(11B,H)=98 Hz.

The spectra correspond to the spectra indicated in WO 2012/163489.

Elemental Analysis:

found, %: C, 27.94, H, 0.78, N, 32.58;

calculated for C₃HBN₃K, %: C, 27.93, H, 0.97, N, 32.54.

EXAMPLE 5 Synthesis of Potassium Monohydridotricyanoborate; K[BH(CN)₃]

Naphthalene (265 mg, 2.07 mmol) is dissolved in THF (8 ml), and anexcess of sodium (about 1.00 g, 43.5 mmol) is added. The mixture isstirred at room temperature for 20 min, during which a dark-greensolution forms. In another flask with PTFE spindle (Young, London),potassium fluorotricyanoborate (150 mg, 1.02 mmol) is dissolved in THF(10 ml); the sodium naphthalide solution is rapidly added dropwise tothis solution. During this addition, the reaction solution rapidlychanges colour to dark yellow, and a precipitate forms. Further sodiumis added to the reaction solution until the latter becomes dark green.The suspension standing above the sodium is removed, and a saturatedK₂CO₃ solution (5.6 g in 5 ml of H₂O) is carefully added. The loweraqueous phase formed is separated off and extracted with THF (10 ml).The combined organic phases are dried over K₂CO₃, and the solvent isremoved. The solid residue is washed with CH₂Cl₂ (2×10 ml), filteredoff, and the colourless solid substance is dried in vacuo.

The yield of potassium hydridotricyanoborate, K[BH(CN)₃], is 75 mg(0.582 mmol, 57%).

The ¹H and ¹¹B NMR spectra correspond to the data indicated in Example4.

EXAMPLE 6 Synthesis of Potassium Monohydridotricyanoborate; K[BH(CN)₃]

1.0 g of Na[BF(CN)₃] (6.8 mmol), 1.0 g of potassium hydride, KH (25.0mmol) and 0.7 g of LiBr (8.08 mmol) are taken up in THF (15 ml), and thesuspension is stirred at 80° C. for 38 hours. i-PrOH and H₂O are addedto the reaction mixture with cooling. Evolution of hydrogen is observedduring this addition. All volatile constituents are subsequently removedunder reduced pressure. The solid is taken up in acetone, a little H₂Oand K₂CO₃ are added, and the mixture is stirred for 15 minutes. Afterthe addition of further K₂CO₃, the organic phase is filtered off. Theacetone is removed in vacuo, and the solid obtained is dried in vacuo.

The yield of K[BH(CN)₃] is 258 mg (2.0 mmol), corresponding to 29%, withrespect to the borate employed.

The ¹H and ¹¹B NMR spectra correspond to those of Example 4.

EXAMPLE 7 Synthesis of Potassium Monohydridotricyanoborate; K[BH(CN)₃]

0.20 g of K[BF(CN)₃] (1.36 mmol), 0.15 g of KH (3.75 mmol) and 0.20 g ofLiBr (2.30 mmol) are taken up in THF (5 ml) and stirred at 8000 for 2days. The suspension is filtered, and the solvent is removed in vacuo.The solid is washed with dichloromethane on a glass frit and dried invacuo. Yield of K[HB(CN)₃]: 40 mg (0.03 mmol), corresponding to 22% withrespect to the K[BF(CN)₃]) employed.

The ¹H and ¹¹B NMR spectra correspond to those of Example 4.

EXAMPLE 8 Synthesis of Tetrabutylammonium Monohydridotricyanoborate;[n-Bu₄N][BH(CN)₃] Via Potassium Monohydridotricyanoborate Intermediate

K[BF(CN)₃](1.5 g, 10.20 mmol) is taken up in NH₃ (10 ml) at −78° C., andpotassium (797 mg, 20.41 mmol) is added in portions. The suspension isstirred at −78° C. for a further 20 minutes and then slowly warmed toroom temperature. The ammonia evaporating is discharged through apressure control valve. The yellow solid obtained is subsequentlydissolved in water (20 ml). An aqueous [n-Bu₄N]OH solution is added tothe solution, and the mixture is extracted with CH₂Cl₂. The solvent isdistilled off, and the residue is taken up in acetone. Undissolvedmaterial is filtered off, and the filtrate is evaporated to dryness.

The yield of [n-Bu₄][BH(CN)₃] is 1.57 g (4.72 mmol), corresponding to46% with respect to the potassium tricyanofluoroborate employed.

¹H{¹¹B}-NMR (solvent: acetone-D₆), δ, ppm: 0.98 t (4CH₃, 12H;³J_(H,H)=7.2 Hz), 1.45 m (4CH₂, 8H), 1.81 m (4CH₂+B—H, 9H). 3.44 m(4CH₂, 8H).

¹¹B-NMR (solvent: acetone-D₆), δ, ppm: −40.0 d, ¹J_(11B,H)=97 Hz.

EXAMPLE 9 One-Pot Synthesis of Potassium Monohydridotricyanoborate;K[BH(CN)₃] from Sodium Tetrafluoroborate by In-Situ Generation ofPotassium Monofluorotricyanoborate

Na[BF₄](4.70 g, 42.78 mmol) is taken up in acetonitrile (6.25 ml),trimethylsilyl cyanide, (CH₃)₂SiCN, (30.0 ml, 225.0 mmol) andtrimethylchlorosilane, (CH₃)₃SiCl, (7.5 ml, 59.4 mmol) are added, andthe mixture is stirred at 100° C. for 3 hours. The reaction mixture iscooled to room temperature, and all volatile constituents are removed invacuo (final pressure about 1·10⁻³ mbar). The residue obtained is driedin a fine vacuum at 120° C. for 12 hours and subsequently taken up inliquid ammonia (40 ml) at −78° C. Freshly cut, oil-free sodium (1.967 g,85.56 mmol) is added in a counterstream of Ar, and the reaction mixtureis stirred at −78° C. for one hour. The reaction mixture is subsequentlywarmed to room temperature. Ammonia evaporating is discharged. The solidremaining is taken up in tetrahydrofuran (THF; 200 ml), and H₂O (15 ml)is added to the suspension. The mixture is then stirred with K₂CO₃ (70g) for 15 minutes. The THF phase is subsequently decanted and driedusing K₂CO₃ (30 g) and filtered. The tetrahydrofuran is removed to aresidual volume of about 5-10 ml using a rotary evaporator at a bathtemperature of 70° C. and a pressure of about 600 mbar. Addition ofCH₂Cl₂ (50 ml) causes K[BH(CN)₃] to precipitate out as brown crudeproduct. This is filtered off, washed with dichloromethane (2×50 ml) anddried in a fine vacuum. According to the NMR data, the crude productcontains 10% of K[BH₂(CN)₂]. The yield of K[BH(CN)₃]⁻ 0.36 THF is 66%(4.35 g, 28.08 mmol).

For the subsequent purification, the crude product is dissolved in 5 mlof acetone, and 50 ml of dichloromethane are added. The depositedprecipitate is filtered off and dried in vacuo (final pressure is about1×10-3 mbar).

The yield for the purified product (beige solid) is 2.61 g (47%).

The ¹H- and ¹¹B-NMR spectra correspond to those of Example 4.

EXAMPLE 10 Synthesis of Tetrabutylammonium Monohydridotricyanoborate;[n-Bu₄N][BH(CN)₃] Via Sodium Monohydridotricyanoborate Intermediate in aOne-Pot Reaction in Ethanol

Na[BF(CN)₃](100 mg, 0.764 mmol) is dissolved in dry ethanol (4 ml), andelemental sodium (100 mg, 4.366 mmol) is added at 0° C. The reactionmixture is stirred at 0° C. for 8 hours. Further sodium (100 mg, 4.366mmol) is subsequently added, and the reaction mixture is heated at theboil for 45 minutes. The reaction mixture is taken up in water (10 ml),and a solution of tetrabutylammonium bromide (350 mg, 1.08 mmol) inwater (5 ml) is added. The tetrabutylammonium hydridotricyanoborateformed is extracted with CH₂Cl₂ (5·3 ml), and the combined organicphases are dried using MgSO₄. The suspension is filtered, and thefiltrate is evaporated to dryness in vacuo, and the residue obtained isdried in a fine vacuum.

Yield: 227 mg (0.683 mmol, 89%)

The ¹H and ¹¹B NMR spectra correspond to those of Example 8.

EXAMPLE 11 Synthesis of Sodium Dihydridodicyanoborate; Na[BH₂(CN)₂]

Na[BF₂(CN)₂](100 mg, 0.80 mmol) is dissolved in NH₃ (2 ml) at −78° C.,and sodium (74 mg, 3.23 mmol) is added. The dark-blue solution is slowlywarmed to room temperature, and the ammonia evaporating in the processis discharged through a bubble counter. Water is added to the residue,and the solution is investigated by ¹¹B-NMR spectroscopy. The spectrumproves conversion to [BH₂(CN)₂] salt (about 55 mol %) and furtherunknown boron-containing species (about 40 mol %). The furtherpurification is carried out by conversion to a [BH₂(CN)₂] salt having anorganic cation, subsequent extraction with an organic solvent andwashing with water and subsequent drying.

¹¹B NMR spectrum of [BH₂(CN)₂] anion:

¹¹B{¹H}-NMR (no lock; solvent: water), δ, ppm: −42.2 (s).

¹¹B-NMR (no lock; solvent: water), δ, ppm: −42.2 t, J_(11B,H)=94.6 Hz.

The NMR data are in accordance with the values of K[BH₂(CN)₂] describedin the literature (WO 2012/163488A1).

EXAMPLE 12 Synthesis of Potassium/Sodium Dihydridodicyanoborate;K/Na[BH₂(CN)₂]

Na[BF₂(CN)₂] (20 mg) is taken up in THF together with KH and NaH(together about 30 equivalents) in an NMR tube with a glass valve havinga Teflon spindle and warmed to 70° C. After 3 days, complete conversioninto the dihydridodicyanoborate salt mixture is observed by NMRspectroscopy.

¹¹B NMR spectrum of [BH₂(CN)₂] anion:

¹¹B{¹H}-NMR (no lock; solvent: THF), δ, ppm: −42.6 (s).

¹¹B-NMR (no lock; solvent: THF), δ, ppm: −42.6 t, ¹J_(11B,H)=95 Hz.

The NMR data are in accordance with the values of K[BH₂(CN)₂] describedin the literature (WO 2012/163488A1).

1. Process for the preparation of compounds of the formula I[Me]⁺[BH_(n)(CN)_(4-n)]⁻  I, where Me denotes an alkali metal and ndenotes 1 or 2, by reaction of a compound of the formula II[Me¹]⁺[BF_(n)(CN)_(4-n)]⁻  II, where Me¹ denotes an alkali metal, whichmay be identical to or different from Me, and n denotes 1 or 2, where nis identical in formula I and formula II, with either a) an alkali metalor alkaline-earth metal Me², where an alkali metal Me² may be identicalto or different from Me or Me¹; or a metal alloy Me²/Me or Me²/Me,where, in the case where Me² is an alkali metal, this alkali metal Me²is different from Me or Me; in an inert-gas atmosphere and in thepresence of a medium which is either capable of generating and/orstabilising solvated electrons or is capable of forming an anion freeradical, if necessary with addition of a proton source, and a metalcation exchange in the case where neither Me² nor Me¹ corresponds to Me,or b) an alkali metal hydride of the formula IIIMe³H  III in an inert-gas atmosphere, where Me³ may be identical to ordifferent from Me or Me¹, without or in the presence of an electrophilicreagent which has affinity to F⁻, and subsequent metal cation exchangein the case where neither Me³ nor Me¹ corresponds to Me.
 2. Processaccording to claim 1, characterised in that the reaction according tovariant a) or b) is followed by a purification step.
 3. Processaccording to claim 1, characterised in that the metal cation exchangetakes place during the purification step.
 4. Process according to claim1, characterised in that the metal cation exchange is carried out byreaction with the compound (Me)₂CO₃ and/or the compound MeHCO₃, where Mecorresponds to the alkali metal Me of the compound of the formula I. 5.Process according to claim 1, characterised in that the reaction of thecompound of the formula II, both in variant a) and in variant b), takesplace in the presence of an organic solvent.
 6. Process according toclaim 1, characterised in that the compound of the formula II isprepared in situ.
 7. Process according to claim 1, characterised in thatthe medium for the generation and/or stabilisation of solvated electronsis selected from liquid ammonia, hexamethylphosphoric triamide, amines,α,ω-diaminoalkanes, alcohols or diols.
 8. Process according to claim 7,characterised in that the medium for the generation and/or stabilisationof solvated electrons is liquid ammonia.
 9. Process according to claim1, characterised in that the medium which is capable of forming anionfree radicals is selected from condensed aromatic compounds.
 10. Processaccording to claim 9, characterised in that the aromatic compound isnaphthalene.
 11. Process according to claim 1, characterised in that theproton source is water.
 12. Process according to claim 1, characterisedin that the (F⁻)-affinitive electrophilic reagent is a lithium ormagnesium salt.
 13. Process according to claim 12, characterised in thatlithium bromide is used.
 14. Process for the preparation of compounds ofthe formula IV[Kt]^(z+) z[BH_(n)(CN)_(4-n)]⁻  IV, where [Kt]^(z+) is an inorganic ororganic cation, z corresponds to the charge of the cation and n denotes1 or 2, by anion exchange, where a salt containing the cation [Kt]^(z+)is reacted with a compound of the formula I[Me]⁺[BH_(n)(CN)_(4-n)]⁻  I, prepared according to claim 1, where Medenotes an alkali metal and n has the same meaning as in the compound ofthe formula IV.